Twist drill



June 1o, 17930. 1., PE'AKES TWIST DRILL Filed' oct 25, 1926 QQ, 8 1./ /ff f f a Patented June 10, 1930 UNITED` STATES PATENT OFFICE y GILBERT L. PEAKES, BLOOMFIEIIJD, NEW JERSEY, ASSIGNOR T0 BAKELITE COR- PORATION, OF NEW YORK, N. Y.,

A CORPORATION 0F DELAWARE l TWIST DRILL Application filed October 23, 1926. Serial No. 143,557.

This invention relates to drills or drill bits for drilling holes, particularly in phenolic condensation products, such as bakelite, redmanol, etc., or in celluloid, hard rubber, casein, and the like.

The ordinary twist drill used in metal working is not suitable for drilling in trans-f parent bakelite, redmanol, etc., because of the rough appearance of the hole produced Vby it, which destroys the transparency of the material where the hole is ldrilled and makes an article of unsightly appearance.

Furthermore, due to the design of the ordinary twist drill, an excessive amount of heat is generated in drilling bakelite, or the'like, which tears the surface of the hole, clogs the drill, makes inaccurate holes fand often breaks the drill or splits the material.

One ofthe objects of the invention is to provide a drill which is. especially adapted for drilling in bakelite, redmanol, Celluloid, casein products and the like.

A special object of this invention is r`to provide a drill for drilling holes in trans? parent varieties ofthe above named substances without marring or clouding the surface of the hole or destroying the transparency of the material where the hole is drilled, or splitting the material.

Another object is to provide a drill for drilling holes in bakelite, redmanol and the like, which can be fed rapidly into the work, and will discharge the chips and cuttings l as rapidly as they are formed. This feature of my invention is of special advantage in drilling bakelite or the like, as the construction of the ordinary metal-cutting twist drill is such that it will not discharge the bakelite chips as rapidly as they are formed, making 'it necessar to withdraw the drill from the hole at requent intervals to remove the chips which have accumulated therein..

This is an important advantage in the use of my drill on automatic or semi-automatic drilling machines as it permits the drills to be fed uniformly into the work to the desired depth and withdrawn when the hole is completed, whereas with the use of ordinary metal-cutting twist drills, it is necessary to provide special cams to withdraw the drills at frequent intervals -to discharge the chips.

In the drilling or cutting of bakelite, and

the like, exceedingly voluminous chips .are formed which expand greatly under the heat of cutting and the heat generated by the friction between the lands of the ordinary drill and the walls of the hole. The bakelite, or other material, although infusble, is softened by the heat of the cutting, and in the use of the ordinary metal twist drill the Walls of the hole are torn or roughly abraded as the metal and chips are forced' over the soft, warm surface. By providing a drill which affords maximum room for the voluminous chips and will discharge them rapidly, land which has no lands rubbing against the walls of the hole, I am able to make a cooler cut and therefore avoid softening and burning or tearing the walls of the hole.

Other objects andv advantages will be pointed out in the specification which to gether with the accompanying drawings discloses a drill capable of securing the object set forth above. v

Referring to the drawings;

Figure l is an outline perspective view of .my improved drill as used in drilling a hole in a transparent block of bakelite.

Figure 2 isla sectional view of the drilled Fi ure '4: is a'sectional view of the drill o the line 4 4 of Figure 1.

Figures 5 and 6 are a side view and antion to the ordinary twist drill whose sharp corners have a tendency to give a scratchy screw thread appearance to the walls of the hole.

For bakelite a zero rake is used, as indicated at 10, to avoid a chipping cut in the bakelite. For Celluloid a slight rake is desirable.

The bakelite and other organic chips or cuttings l are not ordinarily of suiiicient strength to push themselves up the fiute of the drill and out of the hole as steel cuttings do', so that it is desi-rable to use the convolutions of the drill to elevate or discharge the cuttings from the hole. To facilitateV the discharge of the cuttings, and prevent the friction between the chips and drill and the walls of the hole fromscratching and cloeding the hole, the flute 7, of the.

drill, is given a high polish and the pitch is reduced to approximately two diameters, or approximatelyo to the axis -in order to reduce the incline along which the chips must travel. A pitch of two to four diameters or 32 to 52 may, however., be used.

To further facilitatethe discharge of the l cuttings and keep the drilling heat as low as possible,l vthe thickness Aof the metal in the web, namely, between the point 7 in the valley or flute and the same point 7 in the diametrically opposite flute, is reduced, throughout the length of the drill which gives a larger and uniform space in the valley or iiute through which the/ cuttings may travel, than can be given in the twist drills for metal because in those drills enough metal must be retained in the web the land of the ordinary drill, as it has been found that these lands rubbing against the surface of the walls of the hole generate heat and permit the bakelite cuttings to slip between them and the walls of' the hole, which also creates considerable friction and causes burning, tearing and clouding of the walls of the hole.

The point is ground with a front rake suitable to the material being drilled.

To further prevent scratching or cloudl ing the hole,^the drill'has considerable taper back from the rounded point 6 as illustrated at 9 which will allow the drill to run ec.- centrically or diagonally throughthe material without the shank `of the drill or the ridges 8 back of the cutting point catching on the'surface of the hole and causing chat- 1 tering. This reduced 'diameter or taperl back of the point also prevents the drill catching like a screw and feeding itself into the work at a higher rate because of its own pitch. rllhe shank is of smaller diameter than the fluted portion ofthe drill in ordertov allow a hole of greater depth than the iiuted portion to be drilled.

One method of making a drill of this l,

type is to `flatten a portion o-f a round rod by `forging or otherwise, tapering vthe flattened portion outwardly from the rod to the end.'

Each edge of the flattened portion is then cut back from the` ridges `8 to eliminate the lands, the flattened portion uniformly -twisted to produce a pitch of about two diameters,rthe rounded corners 6 ground, the tip sharpened and the chip space polished. It will be understood, however, that the drill may be made by machining from a ,rod, grinding. down fromv a wood bit or in any other suitable manner.

The smooth glazed appearance of the walls of the hole produced by my drill in a block of bakelite 5 is illustrated in Figure 2, and in contrast thereto the .clouded orA4 f'scratched appearance of the hole produced vbakelite 5 is illustrated in Figure 3.

While my drill is especially adapted for drilling clear holes in transparent bakelite and other organic materials, it is also supe- 'rior to prior drillsfor drilling all types of plastic or organic substances where the dimensions, structure, or appearance would be damaged bythe heating edect of imperfect drilling, and its useful application is not limited to transparent varieties of these subby the ordinary drill in a similar block of stances. The drill works with equal facility when the work is stationary and the drill rotated or when the work is rotated andvv produce a hole with unclouded walls in apiece of bakelite or other transparent organic material.

2. A twist drill with sharp ridges, a gradual. slope from the ridges to the flute, a polished flute of reduced section, a taper back from the point and a rounded point with substantially zero rake.. t

3. As an article of manufacture, a twist drill adapted especially to produce a hole in a piece of bakelite or other organic material, having sharp ridges, a gradual slope from the ridges to the flute, a polished iute of reduced section, a taper back from the point, a rounded point with zero rake, and

a shank of smaller diameter than the twisted portion. l

In testimony whereof I have aiixed my signature to this specification.

GILBERT L. PEAKES. 

